Method and device for temperature reduction of exhaust gas by making use of thermal water

ABSTRACT

A system for reducing the temperature of exhaust gas in an incinerator or boiler equipment having an exceedingly small size and avoiding any difficulties caused by damage to the wall surface of a gas cooling chamber due to adherence of sprayed water droplets and deposition of dust. More specifically, pressurized thermal water with a temperature higher than a boiling point of water under atmospheric pressure is sprayed as temperature reduction water into high temperature exhaust gas Gh in a gas cooling chamber or an exhaust gas duct. The temperature reduction of exhaust gas and the removal of acidic gas in the exhaust gas are simultaneously achieved by spraying pressurized thermal water Wt containing an alkaline solution as temperature reduction water into high temperature exhaust gas Gh in the gas cooling chamber or the exhaust gas duct.

This application is a divisional of U.S. Patent application Ser. No.09/639,662, filed Aug. 16, 2000, now U.S. Pat. No. 6,523,811, whichclaims priority of Japanese Application No. JP 11- 8847 filed, Jan. 18,1999. The entire disclosures of the above applications are incorporatedherein by reference.

TECHNICAL FIELD OF THE INVENTION

This invention relates to the treatment of exhaust gas emitted fromcombustion systems such as waste incinerators, boilers and the like, andmore particularly to an improved method and device for reducing thetemperature of exhaust gas to substantially reduce the size of thedevice, to prevent damage to a gas cooling chamber or an exhaust gasduct caused by sprayed water, to eliminate operational difficultiescaused by the deposit of dust, and also to remove acidic gas containedin the exhaust gas.

BACKGROUND OF THE INVENTION

Conventionally, exhaust gas emitted from combustion systems such aswaste incinerators, boilers and the like is diffused into the atmosphereafter being purified by a gas purification device

In some cases of purification treatment, it has been found necessarythat the temperature of the exhaust gas be reduced to an appropriatetemperature, for example, approximately 120-250° C. depending on the gaspurification device used. Conventionally, in such cases, gaspurification devices spray water into the exhaust gas and utilise itsheat capacity and latent heat of evaporation to reduce the temperatureof the exhaust gas.

Referring to FIG. 9 and FIG. 10, examples are shown of a conventionaldevice to reduce the temperature of exhaust gas, wherein 21 is a gascooling chamber, 21 a is an exhaust gas inlet, 21 b is an exhaust gasoutlet, 21 c is an ash outlet, 22 is a temperature reduction water tank,23 is a pressure pump, 24 is a temperature reduction water nozzle, 25 isa temperature control device, 25 a is a temperature detector, 26 is atemperature reduction water volume control valve, 27 is a injectionpump, 28 is an air compressor, 29 is a compressed air tank, 30 is amixer, Gh is high temperature exhaust gas, Gl is low temperature exhaustgas and C is ash.

With reference to the device for reducing the temperature of exhaust gasin FIG. 9, high pressure water from the temperature reduction water tank22, pressurized by the pressure pump 23, is sprayed into the gas coolingchamber 21 through the temperature reduction water nozzle 24 provided inthe vicinity of the exhaust gas inlet 21 a. The temperature of sprayedwater rises in contact with high temperature exhaust gas Gh, and isvaporised to become steam when it reaches its boiling point.

On the other hand, high temperature exhaust gas Gh in the gas coolingchamber 21 is cooled by the heat capacity of the sprayed water, latentheat of evaporation and the heat capacity of the steam, thus loweringthe temperature to a prescribed temperature so as to be led out of theexhaust gas outlet.

The volume of water to be sprayed into the gas cooling chamber 21 iscontrolled by adjusting the opening of the temperature reduction watervolume control valve 26 through the temperature control device 25 inresponse to temperature detecting signals from the temperature detector25 a. The temperature of low temperature exhaust gas G led out of theexhaust gas outlet 21 b is maintained at a desired temperature bycontrolling water volume to be sprayed into the gas cooling chamber 21by means of controlling the volume of water returned to the temperaturereduction water tank 22.

With reference to the device for reducing the temperature of exhaust gasshown in FIG. 10, water sent from the temperature reduction water tank22 by means of the injection pump 27 and high pressured air sent fromthe compressed air tank 29 are mixed for atomisation in the mixer 30.Atomised water is sprayed into the gas cooling chamber 21 from the mixer30, through the temperature reduction water nozzle provided in thevicinity of the exhaust gas inlet 21 a.

Features such as (1) that the temperature of sprayed water rises incontact with high pressure exhaust gas Gh and is vaporised to becomevapour steam when it has reached its boiling point, (2) that hightemperature exhaust gas Gh in the gas cooling chamber 21 is cooled bythe heat capacity of the sprayed water, latent heat of evaporation andheat capacity of the steam vapour, (3) that the water volume to besprayed into the gas cooling chamber 21 is controlled by adjusting theopening of the temperature reduction water volume control valve 26through the temperature control device 25, and (4) that the temperatureof low temperature exhaust gas G is maintained at a desired temperatureby controlling water volume to be sprayed, are all precisely the same asthose features in FIG. 9. The previous devices for the temperaturereduction of exhaust gas shown in FIGS. 9 and 10 are capable of reducingthe temperature of high temperature exhaust gas Gh to a desiredtemperature by utilising low cost water, thus achieving excellent andpractical effects.

There remain, however, a number of difficulties related to theaforementioned prior devices for temperature reduction of exhaust gas,of which, major difficulties include (a) that refractories are damagedby the downflow of water droplets when they hit the wall surface of thegas cooling chaser directly, (b) that stable operation of the gascooling chamber is impaired by dust adhered to and deposited on the wallsurface, and (c) that it is difficult to provide a device fortemperature reduction of exhaust gas having a small size since the gascooling chamber remains large in size.

In the event of a single fluid method wherein only water is utilized, asshown in FIG. 9, difficulties remain in making the atomized temperaturereduction water have particles of micro-sized diameters, even byincreasing the pressure of the water or making improvements in the waternozzle 24. With this method, the diameters of atomised particles oftemperature reduction water normally stay coarse, having diametersaround 70-200 μm, which makes it difficult for the atomised temperaturereduction water to be thoroughly vaporised within a limited space, thuscausing damage to the refractory when water droplets hit the wallsurface of the gas cooling chamber directly.

Even when damage to the refractory is avoided, there is a possibilitythat dust would adhere to and deposit at the surface of the refractorythat is wet with water droplets, that deposits adhered to the surface ofthe refractory would gradually grow, and that the passage resistance ofexhaust gas in the gas cooling chamber would increase and fluctuateconsiderably, thus making the smooth operation of the gas coolingchamber difficult.

With a double fluid method shown in FIG. 10, wherein water andcompressed air are employed, the diameters of atomised particles oftemperature reduction water normally become around 30-100 μm thusreducing the frequency of problems in comparison with the single fluidmethod.

However, this double fluid method is not ideal from the viewpoint ofcost because of the high initial and running costs of compressed airequipment.

Furthermore, the time required before the aforementioned atomisedcooling water reaches its boiling point and evaporates thoroughly isconsiderably long. This means that it becomes necessary for theretention time of exhaust gas in a gas cooling chamber to besufficiently long, thus requiring a gas cooling chamber of a largecapacity.

For example, in the case of an industrial waste incinerator with acapacity to handle incineration disposal of industrial waste ofapproximately 300 T/D (tons per day), assuming high temperature exhaustgas Gh with an exhaust gas volume of 90,000 Nm³/H (flow rate of gas withvolume converted to normal or standard volume) and an inlet exhaust gastemperature of 240° C. is converted to low temperature exhaust gas Gwith an inlet gas temperature of 180° C., a gas cooling chamber of aninternal diameter of approximately 4,800 mm and the height ofapproximately 9,000 mm is required with a device for temperaturereduction of exhaust gas by means of a single fluid method as shown inFIG. 9. Thus, the total height of the device for temperature reductionof exhaust gas including an exhaust gas inlet 21 a, an exhaust gasoutlet 21 b and an ash outlet 21 c would be approximately 180,000 mm.

When designing previous devices for temperature reduction of exhaustgas, the heat load of the gas cooling chamber is normally chosen to havea value of 5,000-10,000 kcal/m³/H (heat value taken away from exhaustgas per unit volume and unit time of a gas cooling chamber in units ofkilocalories per meter cubed per hour). For example, the heat load ofthe gas cooling chamber is chosen to be 7,000 kcal/m³/H.

SUMMARY OF THE INVENTION

The present invention is concerned with solving the aforementionedproblems with the prior devices for temperature reduction of exhaustgas, namely, (a) that, due to coarse particle diameters of atomisedtemperature reduction water, water droplets directly hitting the wallsurface of the gas cooling chamber cause damage to the refractory, and,due to dust adhered to and deposited on the wall surface, the smoothoperation of the gas cooling chamber is disturbed with the single fluidmethod, (b) that pressurized air equipment is required, thus increasingboth initial and running costs with the double fluid method, and (c)that it becomes difficult to make the gas cooling chamber significantlysmaller in size due to the time consumed before atomised water particlesevaporate. Accordingly, it is an object of the present invention toprovide a method and device for effective and economical temperaturereduction of exhaust gas having an exceedingly small size by means ofreducing the diameter of the atomised water particles.

The inventor of the present invention has acquired knowledge throughdesigning, manufacturing and experimenting with numerous devices fortemperature reduction of exhaust gas. For example, the inventor hasfound that with a device for temperature reduction of exhaust gas usingthe single fluid method wherein only water is employed, it is difficultto reduce the particle diameter of atomised temperature reduction watersmaller than approximately 100 μm just by providing an improvedtemperature reduction water nozzle or raising the pressure oftemperature reduction water, as long as a temperature reduction waternozzle is employed for atomisation. Accordingly, it is difficult toprovide a gas cooling chamber having a remarkably reduced volume

The inventor of the present invention, therefore, has departed from theconventional idea of the design of the prior art type of device fortemperature reduction of exhaust gas wherein water of a normaltemperature of approximately 20-30° C. is employed as temperaturereduction water, and heat capacity of water and latent heat ofevaporation are effectively utilized, and has come to the idea of aprocess wherein air-liquid of pressurized water at the boiling point ofwater under atmospheric pressure or pressurized thermal water partlycontaining steam is atomised and injected through a conventionaltemperature reduction nozzle.

When pressurized water of a temperature higher than the boiling point ofwater under atmospheric pressure is used, the heat value equivalent ofthe heat capacity of the water to be utilized for cooling exhaust gas isreduced compared with the prior single fluid method, thus resulting in aslight increase in the water volume required.

However, when said pressurized thermal water is sprayed through atemperature reduction water nozzle into a gas cooling chamber, thereoccurs so-called boiling under reduced pressure in the vicinity of theoutlet of temperature reduction water nozzle, and particle diameters ofatomised water become micro-sized in a range of approximately 3 μm-50μm, and the water rapidly evaporates within a short period of time in agas cooling chamber, thus enabling improvement of the cooling effect ofexhaust gas and allowing the gas cooling chamber to be smaller in size.

The present invention has come into existence based upon the results ofnumerous experiments related to temperature reduction of exhaust gasbased on the aforementioned ideas which go against the conventionaltechnical common sense or practices carried out by others.

In a first embodiment according to the present invention, the presentinvention relates to spraying pressurized thermal water with atemperature higher than the boiling point of water under atmosphericpressure as temperature reduction water into exhaust gas.

In a second embodiment according to the present invention, the presentinvention relates to spraying pressurized thermal water with atemperature higher than the boiling point of water under atmosphericpressure as temperature reduction water into a gas cooling chamber or anexhaust gas duct.

In a third embodiment according to the present invention, thermal watertaken out of a deaerator or continuous blow water of a boiler isutilized as part of the pressurized thermal water.

In a fourth embodiment according to the present invention, pressurizedthermal water partly containing steam is used as temperature reductionwater.

In a fifth embodiment according to the present invention, pressurizedthermal water containing an alkaline solution is used as temperaturereduction water.

In a sixth embodiment according to the present invention, heatedalkaline solution is mixed into the thermal water.

In a seventh embodiment according to the present invention, alkalinesolution is used as an alkaline aqueous solution or alkaline slurrysolution.

In an eighth embodiment according to the present invention, an alkalineaqueous solution containing sodium hydroxide (caustic soda), or analkaline slurry solution containing calcium hydroxide (slaked lime) isused.

In a ninth embodiment according to the present invention, the presentinvention comprises a gas cooling chamber equipped with a gas inlet, agas outlet and an ash outlet, a thermal water tank for storingpressurized thermal water with a temperature higher than the boilingpoint of water under atmospheric pressure, a temperature reduction waternozzle to spray thermal water from the thermal water tank into the gascooling chamber, a temperature reduction water volume control valve toadjust the volume of thermal water to be supplied to the temperaturereduction water nozzle, a temperature detector for low temperatureexhaust gas flowing from the gas outlet, and a temperature controldevice with an opening and closing mechanism for controlling thetemperature reduction water volume control valve in response todetecting signals from the aforementioned temperature detector.

In a tenth embodiment according to the present invention, the presentinvention comprises an exhaust gas duct through which exhaust gas flows,a thermal water tank for storing pressurized thermal water with atemperature higher than the boiling point of water under atmosphericpressure, a temperature reduction water nozzle to spray thermal waterfrom the thermal water tank into the exhaust gas duct, a temperaturereduction water volume control valve to adjust the volume of thermalwater supplied to the temperature reduction water nozzle, a temperaturedetector for low temperature exhaust gas flowing from the exhaust gasduct, and a temperature control device with an opening and closingmechanism for controlling the temperature reduction water volume controlvalve in response to detecting signals from the aforementionedtemperature detector.

In an eleventh embodiment according to the present invention, thermalwater is supplied to the temperature reduction water nozzle by means ofan internal pressure of the thermal water tank.

In a twelfth embodiment according to the present invention, the basicconstitution of the present invention comprises a gas cooling chamberequipped with a gas inlet, a gas outlet and an ash outlet, a thermalwater tank for storing pressurized thermal water with a temperaturehigher than the boiling point of water under atmospheric pressure, analkaline solution tank for storing alkaline solution, a mixer for mixingthermal water from the thermal water tank and alkaline solution from thealkaline solution tank, a temperature reduction water nozzle forspraying thermal water containing alkaline solution from theaforementioned mixer into the gas cooling chamber, a temperaturereduction water volume control valve for adjusting the flow volume ofthermal water containing alkaline solution to be supplied to thetemperature reduction water nozzle, an alkaline solution volume controlvalve for adjusting the flow volume of alkaline solution to be suppliedto the aforementioned mixer, a temperature detector for low temperatureexhaust gas flowing from the gas outlet, an acid gas concentrationdetector for the aforementioned low temperature exhaust gas, atemperature control device with an opening and closing mechanism forcontrolling the temperature reduction water volume control valve bymeans of detecting signals from the aforementioned temperature detector,and an acid gas concentration control device with an opening and closingmechanism for controlling the alkaline solution volume control valve bymeans of detecting signals from the aforementioned acid gasconcentration detector.

In a thirteenth embodiment according to the present invention, analkaline solution heater for heating alkaline solution is installed inthe alkaline solution inlet side of the mixer.

In a fourteenth embodiment according to the present invention, analkaline solution tank is used for the alkaline solution tank forstoring alkaline aqueous solution or alkaline slurry solution.

In a fifteenth embodiment according to the present invention, thepresent invention comprises an exhaust gas duct through which exhaustgas flows, a thermal water tank for storing pressurized thermal waterwith the temperature higher than a boiling point of water underatmospheric pressure, an alkaline solution tank for storing alkalinesolution, a mixer for mixing thermal water from the thermal water tankand alkaline solution from the alkaline solution tank, a temperaturereduction water nozzle for spraying thermal water containing alkalinesolution from the aforementioned mixer into the exhaust gas duct, atemperature reduction water volume control valve for adjusting the flowvolume of thermal water containing alkaline solution to be supplied tothe temperature reduction water nozzle, an alkaline solution volumecontrol valve for adjusting the flow volume of alkaline solution to besupplied to the aforementioned mixer, a temperature detector for lowtemperature exhaust gas flowed from the outlet of the exhaust gas duct,all acid gas concentration detector for the aforementioned lowtemperature exhaust gas, a temperature control device with an openingand closing mechanism for controlling the temperature reduction watervolume in response to detecting signals from the aforementionedtemperature detector, and an acid gas concentration control device withan opening and closing mechanism for controlling the alkaline solutionvolume control valve in response to detecting signals from theaforementioned acid gas concentration detector.

In a sixteenth embodiment according to the present invention, analkaline solution heater for heating alkaline solution is installed inthe alkaline solution inlet side of the mixer.

In a seventeenth embodiment according to the present invention, analkaline solution tank is provided for storing alkaline aqueous solutionor alkaline slurry solution.

Any combustion system such as a waste incinerator, a boiler and the likecan be the emission source of the aforementioned high temperatureexhaust gas, and the present invention is applicable to temperaturereduction of all kinds of exhaust gas from combustion.

The temperature of high temperature exhaust gas Gh supplied to a gascooling chamber can be fixed at the temperature of 150° C.-1000° C., andthe temperature of low temperature exhaust gas G supplied from the gascooling chamber can be fixed at a temperature higher than about 100° C.For example, when the present invention is applied to primary cooling ofexhaust gas, the temperature of high temperature exhaust gas Gh and thetemperature of low temperature exhaust gas G can be fixed atapproximately 900° C.-1000° C. and 150° C.-250° C., respectively. Whenthe present invention is applied to secondary cooling of exhaust gas,the temperature of high temperature exhaust gas Gh and the temperatureof low temperature exhaust gas G can be fixed at approximately 200°C.-400° C. and 120° C.-250° C. respectively.

The aforementioned gas cooling chamber can be formed in either avertical shape or horizontal shape, and its cross section can be of anysuitable shape, such as, for example, a circle, an ellipse or a square.

Similarly, the form of the aforementioned exhaust gas duct can be eitherof long width or short width, and its cross section can be of anysuitable shape, such as, for example, a circle, an ellipse or a square.

The aforementioned pressurized thermal water Wt is water maintained at atemperature higher than the boiling point of water (100° C.) underatmospheric pressure, or so-called water of high pressure and hightemperature. The pressure of the pressurized thermal water Wt can bechosen at values of approximately 1 kg/cm²G 100 kg/cm²G. However, takingthe pressure resistance of a thermal tank 2 into consideration, it isdesirable that it is chosen somewhere between 3-10 kg/cm²G.

Pressurized thermal water Wt can partly contain steam. However, lesssteam content is desirable.

As a heat source for producing thermal water, water vapour from a wasteheat boiler can be utilized if the combustion system, an incinerator,for example, is equipped with a waste heat boiler, and part of thevaporised steam can be utilized when the combustion system is a boiler.

With an incinerator not equipped with a waste heat boiler, either anexhaust heat exchanger is installed to utilise water vapour from theexchanger, or an independent steam or electric boiler of a smallcapacity can be installed.

When a deaerator is attached to the waste heat boiler of an incineratoror a boiler, thermal water produced in the deaerator can be used astemperature reduction water as it is. In this case, a device fortemperature reduction can be constituted inexpensively because all thatis needed for supplying thermal water Wt is installation of a pipe fromthe deaerator.

Furthermore, if a boiler or an incinerator equipped with waste heatboiler is used as a combustion system, continuous blow water from theboiler can be utilized as part of thermal water to be used astemperature reduction water. Most boiler equipment is designed so thatpart of boiler water (thermal water) is discharged outside to stop therise of concentration of corrosion inhibitor and the like in the boilerwater, so that a stable function of the corrosion inhibitor isperformed. Boiler water discharged outside is normally found to bealkaline water of pH 8.5-11.8, having dechlorination or desulfurisationeffects. Therefore, when chemicals are used for dechlorination ordesulfurisation of exhaust gas, the amount of chemicals can be reduced.

If the gas cooling chamber is of a vertical type, it is desired that thetemperature reduction water nozzle for atomising pressurized thermalwater be installed at an upper part and in the vicinity of a gas inletfor high temperature exhaust gas Gh. The installation position of thetemperature reduction water nozzle can be chosen as desired depending onthe type of gas cooling chamber and the number of temperature reductionwater nozzles to be installed. The same feature can be extended to thecase wherein pressurized thermal water is injected inside an exhaust gasduct.

Any kind of suitable construction of nozzle such as water spray nozzles,for example, conventional screw type or collision type nozzles can beutilized.

Further, the number of temperature reduction water nozzles can be chosenas desired depending on such factors as the shape of the gas coolingchamber or exhaust gas duct, the number of ejection apertures installedat a nozzle, and the required ejection volume of thermal water, etc. Forexample, with a device for temperature reduction of exhaust gas for aprior art industrial waste incinerator (having a volume of incinerationof 300 ton/D, a volume of exhaust gas of 90,000 Nm³/H, secondary coolingof exhaust gas (high temperature exhaust gas Gh at 240° C. and lowtemperature exhaust gas G at 180° C.), thermal water (saturated water oftemperature 142.9° C. and pressure 3 kg/m²G), a temperature reductionwater nozzle having three ejection apertures is installed at the upperpart of the gas cooling chamber as described hereafter.

According to the present invention, the temperature and pressure ofthermal water sprayed through a temperature reduction water nozzlebecomes considerably higher than the boiling point of water underatmospheric pressure (100° C.). Abrupt boiling under reduced pressure inthe vicinity of an outlet of the nozzle ejection mouth producesmicro-sized particles which instantly evaporate to water vapour afterspraying, thus causing no direct impact of the wall surface of the gascooling chamber liquid water droplets.

The results of the present invention, thus enable the volume of the gascooling chamber to be small, reducing installation costs and space. Forexample, with a device for temperature reduction of exhaust gas equippedon the outlet side of a waste gas boiler of the aforementioned prior artindustrial waste incinerator, when the temperature of high temperatureexhaust gas is reduced from 240° C. to 180° C., it is found the heatload of the gas cooling chamber can achieve 50,000-150,000 kcal/m³/H.

Namely, compared with the heat load (5,000-10,000 kcal/m³/H) of a gascooling chamber in a prior art device for temperature reduction ofexhaust gas, the device for temperature reduction of exhaust gas in thepresent invention can be chosen at the range of 50,000-150,000kcal/m³/H, thus enabling the volume of the gas cooling chamber to bereduced from ⅕-{fraction (1/15)}.

Furthermore, the present invention allows the device to be constructedso that thermal water is directly sprayed into a high temperatureexhaust gas duct by inserting a temperature reduction water nozzle,without providing a gas cooling chamber.

When thermal water is used for temperature reduction water, the volumeof water sprayed increases slightly comparing with the case where lowtemperature water is used, is conventionally practised, due to thereason that the cooling capacity, which corresponds to the heatcapacity, is lowered. For example, when the temperature of temperaturereduction water with the conventional device for temperature reductionof exhaust gas is kept at 20° C. and the temperature of thermal waterwith the device for temperature reduction of exhaust gas according tothe present invention at 142.9° C. (saturated water of pressure 3kg/cm²G), it is found that approximately 1.2 times the volume of thermalwater is required. This increase, however, does not require a largersize pipe for the thermal water line, thus not requiring much extrainstallation cost.

Thermal water mixed with alkaline solution used as temperature reductionwater is ejected into exhaust gas through a temperature reduction waternozzle to remove hydrogen chloride (HCl) or sulphur oxide (SO₂)contained in the exhaust gas.

The aforementioned alkaline solution can be in the form of either analkaline aqueous solution or an alkaline slurry solution.

The temperature of the alkaline solution mixed in the thermal water isnot necessarily required to be raised by heating when the temperature oftemperature reduction water mixed with said alkaline solution is higherthan the boiling point of water under atmospheric pressure. It is,however, desirable that, when the temperature of temperature reductionwater becomes lower than the boiling point of water under atmosphericpressure by mixing with the alkaline solution, that the temperaturereduction water be heated to a required temperature before the alkalinesolution is mixed into the thermal water.

Any kind of alkaline agent in the aforementioned alkaline solution canbe used. However, when it is used in the form of alkaline aqueoussolution, sodium hydroxide (caustic soda, NaOH) or magnesium hydroxide(Mg(OH)₂) are preferred.

When an alkaline slurry solution is used, sodium hydroxide (slaked lime,Ca (OH)₂), quick lime (CaO), calcium carbonate (CaCO₃), and sodiumcarbonate (Na₂CO₃) are preferred.

The total amount of alkaline agent in the alkaline solution to be mixedinto the aforementioned thermal water is appropriately adjusteddepending on the type and quantity of acidic gas in the exhaust gas andthe temperature of the exhaust gas. Normally, alkaline agents of anequivalent ratio of 0.8-1.5 are mixed into the thermal water.

Further objects, features and advantages of the present invention willbecome apparent from the Detailed Description of Preferred Embodimentswhich follows, when considered together with the attached Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a method and device fortemperature reduction of exhaust gas according to an embodiment of thepresent invention.

FIG. 2 is a partly longitudinal sectional view of a temperaturereduction water nozzle employed according to the present invention.

FIG. 3 is a view taken along the line 1—1 of FIG. 2.

FIG. 4 is a front view of the method and device for temperaturereduction of exhaust gas in accordance with another embodiment of thepresent invention.

FIG. 5 is a view taken along the line 1—1 of FIG. 4.

FIG. 6 is a diagrammatical illustration of a method and device fortemperature reduction of exhaust gas according to a still furtherembodiment of the present invention wherein alkaline aqueous solution ismixed into the thermal water.

FIG. 7 is a diagrammatical illustration of a method and device fortemperature reduction of exhaust gas according to yet another embodimentof the present invention wherein alkaline slurry solution is mixed intothe thermal water.

FIG. 8 is a curve showing removal characteristics of acidic gas in theexhaust gas according to the present invention.

FIG. 9 is a diagram illustrating a device for temperature reduction ofexhaust gas according to the prior art.

FIG. 10 is a diagram illustrating another device for temperaturereduction of exhaust gas according to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The reference numerals, as used in the preceding description and in theFigs. are as follows: 1 is a gas cooling chamber, 1 a an exhaust gasinlet, 1 b an exhaust gas outlet, 1 c an ash outlet, 1 d airtightretaining device, 2 a thermal water tank, 3 a pump, 4 a temperaturereduction water nozzle, 4 a an ejection mouth, 4 b a main body, 4 c ascrew, 4 d a water lead-in hole, 5 a temperature control device, 5 a anexhaust gas temperature detector on the outlet side, 6 a water reductionvolume control valve, Gh high temperature exhaust gas, Gl lowtemperature exhaust gas, S heated steam, C ash, Wt thermal water, 7 aduct, 7 a a flange for fixing a temperature reduction water nozzle, 7 ba duct outlet, 8 an alkaline solution tank, 8 b a stirrer, 9 an alkalinesolution pump, 10 an alkaline solution flow volume control valve, 11 analkaline solution heater, 11 a a drain valve, 12 a mixer, 13 an acid gasconcentration detector for low temperature exhaust gas, Wp alkalinesolution, P alkaline agents, W₁ water, and Sl steam for heating.

FIG. 1 illustrates an embodiment of the method and device fortemperature reduction of an exhaust gas according to the presentinvention, wherein 1 designates a gas cooling chamber, 1 a an exhaustgas inlet, 1 b an exhaust gas outlet, 1 c an ash outlet, 1 d an airtightretaining device, 2 a thermal water tank, 3 a pump, 4 a temperaturereduction water nozzle, 5 a temperature control device, 5 a an exhaustgas temperature detector on the outlet side, 5 b an exhaust gastemperature detector on the inlet side, 6 a temperature reduction watervolume control valve, Gh high temperature exhaust gas, G low temperatureexhaust gas, S heated steam, at thermal water, and C ash.

Referring now to FIG. 1, a gas cooling chamber 1 is in the form of atower in which a wall surface is formed with an adiabatic structure byemploying a known heat insulating material.

Also provided are an exhaust gas outlet 1 a on the upper part of a gascooling chamber 1, an exhaust gas outlet 1 b on the lower part, an ashoutlet at the lower end of a reversed conical part downwards 1 c, and anairtight retaining device (an open/closing damper) 1 d, respectively.

The same principals of construction and operation would apply to formsand sectional shapes of the gas cooling chamber other than the towertype illustrated in FIG. 1.

In reference to this embodiment of the present invention, hightemperature exhaust gas Gh (temperature of approximately 240° C. and aflow volume of approximately 90,000 Nm³/H) emitted from a waste heatboiler (not illustrated) of an industrial waste incinerator is led intothe aforementioned gas cooling chamber 1, approximately 150° C.-1,000°C. is the desired temperature for high temperature exhaust gas as anobject of temperature reduction.

Further, the exhaust gas that is the object of temperature reduction canbe exhaust gas from any combustion system, and there is no specificcondition on its flow volume.

A thermal water tank 2 is in the form of a heat and pressure resistingmetal tank having a required capacity and protected by a heat insulatingmaterial.

Water of high temperature (pressurized thermal water Wt) with thetemperature higher than a boiling point (100° C.) under atmosphericpressure is stored in said thermal tank 2. In the embodiment, thermalwater Wt of high temperature and high pressure having the temperature of142.0° C. (saturated water at pressure 3 kg/cm²G) is stored in a thermaltank 2 with pressure resistance of 10 kg/cm².

In reference to the embodiment shown in FIG. 1, steam S for heating isled into a thermal tank 2 from a waste boiler (not illustrated)installed with an industrial waste incinerator, and the temperature ofthermal water Wt is retained at the aforementioned 142.9° C. value bymeans of said heated steam S.

A heat source of thermal water Wt can be constructed so that heat from aseparately provided burner or from an electric heater is utilized, inaddition to the arrangement wherein steam from a boiler is utilized, asshown in the present embodiment.

When a boiler is provided, so-called continuous blow water from theboiler can be utilized as part of the thermal water. When a deaerator isprovided with the boiler, water of high temperature and high pressureproduced inside the deaerator can also be utilized as thermal water Wtor as part of thermal water Wt.

The aforementioned pump 3 is designed to supply thermal water Wt to atemperature reduction water nozzle 4. Said pump 4 is to be installedonly when it is required in relation to pressure loss of the pipebetween thermal tank 2 and temperature reduction water nozzle 4 and alsoin relation to a potential head of the temperature reduction waternozzle 4.

As illustrated in FIG. 2 and FIG. 3, the aforementioned nozzle 4 is of aknown hollow cone type. In reference to this further embodimentaccording to the present invention, a nozzle equipped with 3 ejectionapertures 4 a at intervals of the angle of 120° is mounted at the centerof the upper part of the gas cooling chamber 1.

Referring to FIG. 2, 4 b is a main body, 4 c a screw and 4 d a waterlead-in hole.

An ejection angle of each ejection month 4 a of the temperaturereduction water nozzle 4 is fixed approximately at 60° (under theejection pressure of 3 kgf/cm²) and the flow volume is fixedapproximately at 3.8 l/min (under the ejection pressure of 3 kgf/cm²).

Further, in reference to the embodiment shown in FIG. 2, a hollow conetype spraying nozzle is utilized as a temperature reduction water nozzle4. However, any kind, type or structure of nozzle 4 can be chosen forapplying to the present invention as long as it enables spraying waterwith a particle diameter of 190-300 μm from previous water with normaltemperature under a pressure of 2-3 kgf/cm².

A temperature control device 5 receives temperature detection signalsfrom an exhaust gas temperature detector 5 b installed on the inlet sideand an exhaust gas temperature detector 5 a installed on the outletside, adjusts the volume of thermal water to be sprayed into a gascooling chamber 1 by means of an opening and closing mechanism tocontrol a temperature reduction water volume valve 6 and retain thetemperature of low temperature exhaust gas G emitted from the exhaustgas outlet 1 b at set values.

In reference to embodiment according to the present invention,thermostat type temperature detectors are employed for the exhaust gastemperature detectors 5 a, 5 b. However, such detectors can be replacedby any other suitable kind of detector.

In reference to this embodiment according to the present invention, atemperature reduction water volume control valve 6 is provided in apassageway for supplying thermal water. However, as illustrated in theprevious FIG. 6, a temperature reduction water volume control valve 6can be provided in a return passageway for thermal water Wt. Any methodof control can be applied as long as the volume of thermal water to besupplied to the temperature reduction water nozzle is able to becontrolled.

At the time when the temperature of high temperature exhaust gas Gh froma combustion system is reduced, thermal water Wt in a thermal tank 2 issent to a temperature reduction water nozzle 4 by means of internalpressure in the thermal tank 2 and/or pressurized power of water, andsprayed into high temperature exhaust gas Gh through the temperaturereduction water nozzle.

Thermal water Wt sprayed through a temperature reduction water nozzle 4becomes pressurized water having a temperature considerably higher thana boiling point (100° C.) under atmospheric pressure, and abruptly boilsunder the reduced pressure in the vicinity of an ejection mouth 4 a ofthe temperature reduction water nozzle 4, producing atomised sprayparticles having diameters of 50-5 μm, and turns to steam instantly whenevaporated, thus realising cooling of exhaust gas by means of heatexchange with high temperature exhaust gas Gh in the gas cooling chamber1.

Low temperature exhaust gas G cooled to the prescribed temperature isextracted through an exhaust gas outlet 1 b outside, while ash C (dustand the like), separated from exhaust gas, is discharged outside throughan ash outlet 1 c.

EXAMPLE 1

A tower type device for temperature reduction equipped with acylindrically shaped gas cooling chamber 1 is formed to reduce thetemperature of high temperature exhaust gas Gh having the exhaust gasflow volume of 90,000 Nm³/H (exhaust gas from a waste heat boilerequipped with an industrial waste incinerator) and a temperature of 240°C. to a temperature of 180° C. Under conditions that the temperature ofthermal water is 142.9° C. (saturated water of pressure 3 kg/cm² G), andthe volume of thermal water to be sprayed is 2.5 ton/hr, the requiredcapacity of the gas cooling chamber 1 reaches 3000 mm in an internaldiameter and 6000 mm in height, allowing the aforementioned hightemperature exhaust gas Gh to be turned sufficiently to low temperatureexhaust gas G of the prescribed temperature (180° C.) by utilising gascooling chamber 1.

When exhaust gas under same conditions is treated with a previous towertype temperature reduction device (water of 20° C. and the volume ofwater to be sprayed approximately 2 ton/hr), a capacity of approximately4800 mm×9000 mm was required for the gas cooling chamber, while gascooling chamber 1 according to the present invention is found to be ableto be remarkably smaller in size.

According to the present invention, the volume of thermal water Wt to besprayed increases approximately by 20% compared with the prior artwherein water at 20° C. is employed.

According to the present invention, no difficulties have occurred suchas damage to the refractory due to adherence or deposit of dust and thelike caused by adherence of water droplets to the wall surface of thegas cooling chamber, enabling highly stable and continuous temperaturereduction of high temperature exhaust gas.

FIG. 4 and FIG. 5 illustrate another embodiment according to the presentinvention for a method and device for temperature reduction of exhaustgas, wherein thermal water is sprayed into high temperature exhaust gasGh in a duct 7 through a temperature reduction water nozzle 4 attachedto a flange 7 a. The flange 7 a fixes the temperature reduction waternozzle 4 to the side of an exhaust gas duct 7 for the purpose of leadingout high temperature exhaust gas Gh emitted out of a waste incinerator.

Referring now to the embodiment of the present invention shown in FIG. 4and FIG. 5, the construction remains exactly same as the equipment shownin FIG. 1 and FIG. 2, except that the gas cooling chamber 1 in theembodiment shown in FIG. 1 and FIG. 2 is replaced by a vertical typeexhaust gas duct 7.

EXAMPLE 2

If saturated water of 142.9° C. and 3 kg/cm²G is used as thermal waterto be sprayed, the internal diameter of the duct is 2000 mm and thelength of the duct is 7000 mm. By spraying thermal water Wt of 3.4ton/hr into the duct 7 through a temperature reduction water nozzle 4,high temperature exhaust gas Gh of 90000 Nm³/H and 240° C. was able tobe continuously converted to low temperature exhaust gas G ofapproximately 180° C. at the duct outlet 7 b.

No adherence of water droplets to the inner surface of the duct 7 wasobserved, and accordingly no adherence and deposit of dust and the likecaused by the adherence of water droplets was observed.

Referring to FIG. 6 and FIG. 7 according to the present invention, thereis illustrated a third embodiment for the method and device fortemperature reduction of exhaust gas, wherein the temperature of exhaustgas is reduced and an acid component in the exhaust gas issimultaneously removed (or neutralised) by means of spraying alkalinethermal water Wt into high temperature exhaust gas Gh in the gas coolingchamber 1 through a temperature reduction water nozzle 4.

Referring to FIG. 6 and FIG. 7, 8 is an alkaline solution tank, 8 a analkaline agent feeding device, 8 b a stirrer, 9 an alkaline solutionpump, 10 an alkaline solution flow volume control valve, 11 an alkalinesolution heater, 11 a a drain emission valve, 12 a mixer for thermalwater Wt and alkaline solution Wp, 13 an acid gas concentration controldevice, 13 a an acid gas concentration detector for low temperatureexhaust gas Gl, Sl steam for heating, P alkaline agent, Wl Water and Wpalkaline solution. Excluding these components, all other equipment anddevices remain exactly the same as those shown in FIG. 1 and FIG. 2.

Referring to FIG. 6, alkaline aqueous solution is used for alkalinesolution Wp to be mixed into thermal water Wt. For example, alkalineaqueous solution, for which alkaline agent P, such as sodium hydroxide(caustic soda, NaOH) and the like dissolved into water Wl, is stored inan alkaline solution tank 8.

Alkaline agent P that constitutes the alkaline aqueous solution is notlimited to the aforementioned sodium hydroxide as long as the agent iswater soluble. For example, magnesium hydroxide (Mg(OH)₂) and the likecan also be used.

Furthermore, the concentration of alkaline agent in the alkaline aqueoussolution stored in the tank 8 is appropriately chosen depending on thetemperature of water W₁ or solubility of the alkaline agent P used inwater W₁. When sodium hydroxide is used as alkaline agent P, thealkaline concentration is chosen at a concentration of 29-30%.

Referring now to the aforementioned FIG. 7, alkaline slurry solution isused as the alkaline solution Wp to be mixed into thermal water Wt. Forinstance, the solid-liquid mixed body (slurry) wherein alkaline P suchas calcium hydroxide (slaked lime Ca(OH)₂) and the like is suspendeddispersively into water W₁ stored in an alkaline solution tank 8.

Furthermore, alkaline agent P is not limited to the aforementionedcalcium hydroxide. For example, slaked lime (CaO), calcium carbonate(CaCO₃), sodium carbonate (Na₂CO₃) and the like, can also be used.

The quantity of alkaline solution Wp to be mixed into the aforementionedthermal water Wt is adjusted by a mechanism to control alkaline solutionflow volume control valve 10 by opening and closing with an acid gasconcentration control device 13 by receiving detection signals from anacid gas concentration detector 13 a in low temperature exhaust gas G,whereby acidic gas concentration in the aforementioned low temperatureexhaust gas G is maintained at a prescribed value.

The quantity of alkaline solution Wp to be sent to the thermal water Wtis determined with reference to the temperature of low temperatureexhaust gas G, the type of acid gas to be removed, the targeted removalrate of acid gas, and the like. Normally, 1.0-1.5 times volume ofalkaline agent P in an equivalent ratio to the volume of acidic gas tobe removed in the exhaust gas is mixed into thermal water Wt.

The aforementioned alkaline solution heater 11 is used to heat alkalinesolution Wp to be mixed into thermal water Wt to a prescribedtemperature, thus preventing the temperature of alkaline temperaturereduction water flowing out of a mixer 12 from being exceedingly low.

When alkaline solution Wp is small in amount or the temperature ofalkaline solution is comparatively low (for example, 80-90° C.),turbulence in the thermal water Wt occurs with less frequency at thetime of mixing. Accordingly, in such a case, the installation of theaforementioned alkaline solution heater 11 can be omitted.

Referring to the embodiment shown in FIG. 6 and FIG. 7, alkalinetemperature reduction water is ejected into a gas cooling chamber 1.However, needless to say, alkaline temperature reduction water can beejected into an exhaust gas duct 7 shown in FIG. 4 and FIG. 5 instead ofthe aforementioned gas cooling chamber 1.

EXAMPLE 3

A tower type device for temperature reduction equipped with acylindrically shaped gas cooling chamber is formed to reduce thetemperature of 240° C. of high temperature exhaust gas Gh having anexhaust gas flow volume of 90,000 Nm³/h (HCl concentration of exhaustgas from the waste heat boiler of the industrial waste incinerator 800ppm) to temperature of 180° C. Under conditions wherein the temperatureof thermal water Wt is 142.9° C. (saturated water of pressure 3 kg/m²G),the temperature of alkaline solution Wp (NaOH aqueous solution ofconcentration 25%) Wp is 25° C., the supply volume of thermal water Wtis 1.9 ton/h, the supply volume of alkaline solution Wp is 0.606 ton/h,the supply volume of alkaline thermal water to be sprayed isapproximately 2.56 ton/h, the required capacity of gas cooling chamber 1reaches 3000 mm in the internal diameter and 6000 mm in height, allowingthe temperature of the aforementioned high temperature exhaust gas Gh tobe reduced sufficiently to the prescribed temperature (180° C.), to turnit to low temperature exhaust gas G.

The volume of alkaline agent P to be supplied to the HCl volume in theexhaust gas is found, then, to be 1.0 at an equivalent ratio, while theremoval rate of HCl detected by an acidic gas concentration detector 13a is approximately 93% at the time when the temperature of lowtemperature exhaust gas G is 180° C.

The volume of alkaline solution Wp to be supplied is calculated asfollows: the HCl volume in the exhaust gas of 90,000 Nm³/h, having anHCl concentration of 800 ppm, is 9×104×800×10⁻⁶=72 Nm³/h.

An equivalent/h of HCl of 72 Nm³/h is 72/22.4=3.214 kmol. Since theequivalent ratio is 1, an equivalent/h of NaOH to be supplied becomes214 kmol/hr. When NaOH of an equivalent/hr is supplied with NaOH aqueoussolution Wp, the supply volume of NaOH aqueous solution becomes 40kg/kmol×3.214 kmol/h×100/25=606 kg/h.

The reaction formulas for the removal of acidic gas in exhaust gas bymeans of spraying the aforementioned NaOH aqueous solution are asfollows:

NaOH+HCl=NaCl+H₂O

NaOH+SO₂+½O₂=Na₂SO₄+H₂O

The NaCl and the like produced are after-treated by means ofelectrolysis and the like. Since these methods of treatment are alreadyknown, a detailed explanation is omitted.

Taking into consideration the external turbulence of the thermal waterWt at the time of mixing alkaline solution (25% NaOH solution) Wp of thenormal temperature (25° C.), the aforementioned alkaline solution Wp isfirst heated to a temperature of approximately 80° C. by an alkalinesolution heater 11, and then supplied to a mixer 12. However, even whenthe heater 11 is not in use, no particular (difficulties occurred exceptthat the volume of sprayed water through temperature reduction waternozzle 4 was slightly lowered due to the reason that the temperature ofthe alkaline thermal water was reduced at the outlet side of the mixer11.

When acid gas of high concentration is contained in the exhaust gas, themixing volume of alkaline solution Wp increases, thus further loweringthe temperature of thermal water Wt after mixing. However, it has becomeapparent that the situation can be resolved by fixing the temperature ofthermal water Wt slightly higher before mixing without installing aheater 11.

Referring to FIG. 8 in the Example 3, changes in the removal rate ofacid gas (HCl) is shown when the supply volume of NaOH aqueous solutionWp to be fed to a mixer changes. Curve A represents values when thetemperature of low temperature gas G is fixed at 180° C., while curve Brepresents values when it is fixed at 150° C. The vertical axis of thecurve is for acid gas removal rate (%), while the transverse axis is forthe supply volume of NaOH shown in an equivalent ratio. As clearlyindicated in FIG. 8, the lower the temperature of low temperatureexhaust gas the better the improvements of the removal rate. The table 1shown below indicates the concrete numerical values measured with theembodiment illustrated in FIG. 8.

TABLE 1 Equivalent ratio 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1 HCl 4050 60 70 80 89 96 99 100 Removal rate % 2 HCl Removal rate % 39 48 5766 75 85 93 97 99 1 Temperature of low temperature exhaust gas 150° C.2 Temperature of low temperature exhaust gas 180° C.

With reference to the present invention, since pressurized thermal wateris in use as temperature reduction water, sprayed thermal water boilsabruptly in the vicinity of an ejection aperture of the temperaturereduction water nozzle, thus producing atomised particles havingdiameters up to approximately 10 μm, Which turn to steam instantly.

Accordingly, troubles caused by sprayed thermal water in the form ofwater droplets directly hitting and adhering to the wall surface of agas cooling chamber are not seen, thus eliminating damage to the wallsurface of the gas cooling chamber due to the adherence of waterdroplets and difficulties due to the deposition of dust.

Furthermore, cooling performance of sprayed water is greatly improveddue to instant evaporation of sprayed thermal water, thus enabling aremarkable reduction in size of the gas cooling chamber. With regards tothe previous gas cooling chamber that utilized water of normaltemperature as temperature reduction water, the heat load of the gascooling chamber is normally approximately 5,000-15,000 kcal/m³/H,whereas with regard to the gas cooling chamber according to the presentinvention, it is found possible to raise the heat load of the gascooling chamber to 50,000-150,000 kcal/m³/H. This enables a remarkablereduction in size of the gas cooling chamber.

Furthermore, when sufficient pressure is found in the thermal watertank, a temperature boosting pump is not required. Therefore, thefacilities can be constructed simply, thus allowing a remarkablereduction in running costs.

In the case where an incinerator or a boiler is equipped with adeaerator, thermal water of the deaerator can be utilized as it is. Theonly equipment that is needed for temperature reduction water is pipesfrom a temperature reduction water nozzle and a deaerator. This alsoallows inexpensive construction of the equipment.

Owing to the fact that the volume of the gas cooling chamber can be madesmall and thermal water can be sprayed into a high temperature exhaustduct without installing a gas cooling chamber, installation costs can beremarkably reduced.

Furthermore, with an incinerator equipped with a boiler and a waste heatboiler, the volume of chemical agents to be used for the equipment fordesalinisation and desulfurisation of exhaust gas can also be reduced.

In the event that alkaline thermal water is supplied to a temperaturereduction water nozzle, a high removal rate of acidic gas contained inexhaust gas can be achieved with less alkaline agent, thus making theacidic gas removal equipment installed on the downstream side of thedevice for temperature reduction of exhaust gas smaller in size as wellas considerably reducing the amount of agents to be used.

Furthermore, alkaline solution to be mixed into the thermal water is notrequired to be heated to a high temperature. The stable operation of thedevice for temperature reduction of exhaust gas can be realised byfixing the temperature of thermal water slightly higher while mixingalkaline solution of normal temperature into the thermal water.

As explained above, the present invention achieves excellent andpractical effects.

While the present invention has been explained by means of certainpreferred embodiments one of ordinary skill in the art will recognisethat additions, deletions, modifications, substitutions and improvementscan be made while remaining within the scope of the appended claims.

What is claimed is:
 1. A method for reducing the temperature of exhaust gas flowing from an exhaust gas outlet, comprising the steps of: (1) providing pressurized water with a temperature higher than a boiling point of water under atmospheric pressure, wherein the water contains alkaline agents; (2) spraying the water of step (1), into a gas cooling chamber having a wall surface and containing exhaust gas, with a temperature reduction water nozzle installed at an upper part of the gas cooling chamber in the vicinity of a gas inlet for the exhaust gas to produce micro-sized particles of atomized water; (3) evaporating the micro-sized particles of atomized water so that there is no direct impact on the wall surface of the gas cooling chamber; and (4) detecting a temperature of exhaust gas flowing from the exhaust gas outlet and controlling said temperature by controlling a volume of water sprayed into the exhaust gas in step (2).
 2. A method for reducing the temperature of exhaust gas flowing from an exhaust gas outlet, comprising the steps of: (1) providing pressurized water with a temperature higher than a boiling point of water under atmospheric pressure, wherein the water contains alkaline agents; (2) spraying the water of step (1), into an exhaust gas duct having an inside and containing exhaust gas, with a temperature reduction water nozzle installed at an upper part of the exhaust gas duct in the vicinity of a gas inlet for the exhaust gas to produce micro-sized particles of atomized water; (3) evaporating the micro-sized particles of atomized water so that there is no direct impact on the inside of the exhaust gas duct; and (4) detecting a temperature of exhaust gas flowing from the exhaust gas outlet and controlling said temperature by controlling the volume of volume of water sprayed into the exhaust gas in step (2).
 3. A method according to claim 1, wherein said step (1) further comprises taking water out of a deaerator or taking continuous blow water from a boiler.
 4. A method according to claim 2, wherein said step (1) further comprises taking water out of a deaerator or taking continuous blow water from a boiler.
 5. A method according to claim 1, wherein the micro-sized particles have diameters in a range of approximately 3 μm-50 μm.
 6. A method according to claim 2, wherein the micro-sized particles have diameters in a range of approximately 3 μm-50 μm.
 7. A method according to claim 1, wherein the micro-sized particles have diameters up to approximately 10 μm.
 8. A method according to claim 2, wherein the micro-sized particles have diameters up to approximately 10 μm. 